Hydraulic apparatus for providing a differential pressure



Sept. 23,- 1958 J. J. TUER 2,853,091 HYDRAULIC APPARATUS FOR PROVIDING A DIFFERENTIAL PRESSURE Filed May 13, 1955 INVENTOR JoHN J. Tux-32 ATTORNBG Ilnited States Patent Office HYDRAULIC APPARATUS FOR PROVIDING A DIFFERENTIAL PRESSURE John .loseph Tner, Langley, England, assignor to D. Napier & Son Limited, London, England, a British company Application May 13, 1955, Serial No. 508,282 Claims priority, application Great Britain May 25, 1954 4 Claims. (Cl. 137100) This invention relates to hydraulic apparatus for pro viding a differential pressure which varies with variations in the difference between two main pressure values.

It is an object of the invention to provide an improved apparatus of this kind which will be simple to manufacture and accurate in operation and it is a further object to provide apparatus which produces a differential pressure which always exceeds a datum pressure irrespective of which of the two main pressure values is greater at any instant.

According to the invention hydraulic apparatus of the kind referred to comprises a valve including two main pressure chambers and a valve piston assembly provided with two main piston surfaces in said main pressure chambers, these main piston surfaces being acted upon respectively by the two main pressures so as to urge the valve piston assembly in opposite directions, a third differential pressure chamber and a third differential piston surface in said chamber which is acted upon by fluid at the differential pressure in a direction to balance the out-of-balance forces acting on the main piston surfaces a fluid control valve associated with the valve piston assembly and arranged to control the admission of hydraulic fluid to the differential pressure chamber from a source of hydraulic fluid under pressure, and the escape of fluid therefrom, so as to maintain in balance the hydraulic forces acting on the piston assembly, and a differential pressure line connected to said differential pressure chamber.

Particularly when one of the main pressure values is liable to vary between values greater and less than the other main pressure, the apparatus preferably includes a second differential piston surface, pressure on which produces a force on the valve piston assembly in a direction opposite to the force applied by the pressure on the first differential piston surface, means for connecting one or other of the differential pressure chambers selectively to a source of hydraulic pressure fluid through a fluid control valve operated by movements of the valve piston assembly, and means for selectively connecting the same differential pressure chamber to the differential pressure line, and for permitting the escape of fluid from the other differential pressure chamber.

Preferably the source of hydraulic pressure from which fluid is supplied to the differential pressure chamber or chambers, is constituted by a conduit connected to whichever of the main pressure lines is at the higher pressure at any instant.

In a preferred construction the apparatus comprises two hydraulic cylinders each containing a piston, which is mechanically connected to the other piston, means for admitting hydraulic fluid under pressure from the two main pressure lines to one end of each of the two cylinders, which thus constitute the main pressure chambers, valve means operated or constituted by each of said pistons and arranged to control the supply of hydraulic fluid from each of the main pressure lines to the other end of each of the two cylinders which thus constitute the 2,853,091 Patented Sept. 23, 1958 differential pressure chambers, relief valves also operated or constituted by the said pistons and arranged selectively to control the escape of fluid from the differential pressure chambers, and means for connecting whichever of the two main pressure chambers is at any instant at higher pressure to the differential pressure line.

Preferably in this case the two cylinders are arranged in line with one another, and the main pressure chambers are arranged at opposite ends of the two cylinders, and the two pistons are connected by a free compression rod bearing on their adjacent faces, and making a fluid tight fit with a partition wall or the equivalent between the cylinders, the ends of the compression rod being formed to make substantially only point contact with the pistons, and the apparatus includes pressure balancing plungers whose cross-sectional areas are equal to that of the compression rod, and which are each arranged to make substantially point contact with the remote face of one of the pistons, and are acted upon-each at their ends remote from the respective pistons by the pressure in the main pressure line which is connected to the remote face of the other piston.

It will be understood that the invention is therefore particularly applicable to hydraulic torque meters for use with transmission mechanism in which the direction of torque transmission is liable to be reversed.

The invention may be performed in various different ways but one specific embodiment will now be described by way of example with reference to the accompanying drawing, as applied to torque measuring apparatus for use in an aircraft transmission mechanism between a power unit and an aircraft propeller.

The torque measuring apparatus comprises a reaction member 10 connected to a reaction element in the transmission gearing (not illustrated) and to a movable piston 11 in a hydraulic chamber 12, the opposite ends of the chamber 12 being connected to two main pressure bydraulic galleries 13 and 14, the arrangement being such that the reaction torque can be measured by determining the differential pressure between the two galleries 13 and 14 which constitute main pressure lines. To this end the piston 11 is formed with control ports 15 and 16 associated with inlet ports 17 and 18, to which hydraulic fluid is supplied under pressure from a pump 19, such that when the piston is moved in either direction due to variations in the reaction load on the member 11, one or other of the ports 15 and 16 opens to admit pressure fluid to the respective end of the chamber 12, so as to resist this load. At the same time the piston 11 uncovers one of a pair of relief ports 20, 21, and thus connects the opposite end of the chamber to relief. One or other of the pressure galleries 13 and 14 therefore contains hydraulic fluid at a pressure which varies in accordance with variations in the transmitted torque while the other gallery will be at atmospheric or other low pressure. If

the direction of torque transmission is reversed, the pressure conditions in the galleries 13 and 14 will be reversed.

The hydraulic apparatus in accordance with the present invention comprises two coaxial cylindrical chambers 25, 26, of equal cross section, the remote ends of which are connected respectively to the two galleries 13 and 14,

by conduits 27, 28 and thus consitute main pressure chambers 29, 30 while the adjacent ends of the two chambers are connected to a differential pressure line 31 through a pressure selective valve 32, and constitute differential pressure chambers 33, 34. The pressure selecting valve is arranged to connect which ever of the two differential pressure chambers 33, 34, is at any moment at a higher pressure to the differential pressure line 31 and to isolate the other chamber from this line, and comprises a valve chamber, the opposite ends of which are connected to the adjacent ends of the two differ-ential chambers 33, 34 while a mid-point in the chamber is connected to the differential pressure line 31. A free piston 35 in the valve chamber operates in the manner of a shuttle valveto make the desired hydraulic connection. The differential pressure line 31 isv connected to a pressure sensitive device 36 of any known kind'which provides anindication of the pressure in the line, and thus of the torque being transmitted by the transmission gearing.

Each of'the main cylindrical chambers 25,- 26, contains a free piston 37, 38, each having an end surface 8, 9 which constitutes a main piston surface, and an interconnecting compressionrod 39 extends through fluidtight seals in the adjacent endsrofthe chambers and bears on the adjacent faces of the pistons. interconnecting rod .39 are domed, and thus make substantially point contact withthe faces of the pistons 37, 38.

Each piston 37, 38 in the main. cylindrical chambers is formed with a control port 41, 42, in its peripheral surface which communicates through a drilling 43, 44, in the piston with the face of the piston adjacent the inner end of the chamber, which constitutes the respective differential pressure chamber 33 or 34. The main pressure gallery 13 or 14 which is connected to each main pressure chamber 29 or 30 is also connected to a pressure port 45, 46 in the side wall of the chamber spaced somewhat from the outer end thereof, and a second relief port 47, 48 in the side wall of each chamber adjacent the inner end thereof communicates with a relief conduit 49 which in the present instance is maintained substantially at atmospheric pressure. The longitudinal displacement between these pressure and relief ports 45, 47, and 46, 48, in the side wall of each cylindrical chamber, and between the control ports 41, 42 in the pistons and the inner faces'51, 52 thereof (which constitute the first and second differential piston surfaces) is so arranged that at one intermediate position of each free piston both the pressureand relief ports in the side wall of the respective chamber are cracking or just on the point of opening while movement of the piston in one direction or the other from this intermediate position causes one of the ports to open further while the other port becomes closed, and vice 'versa. The ports 45, 47, 48, 41 and 42 therefore together constitute a fluid control valve, controlling the pressure in thediiferential pressure chambers 33 and 34.

Means are also provided for. hydraulically balancing the valve piston assembly comprising the two free pistons 37, 38 and the interconnecting rod 39. To this end a pressure balancing plunger 55, 56 is arranged to pass through a gland in the remote ends of each of the two main pressure chambers 29, 30, and the outer ends of these plungers 55, 56, are arranged in auxiliary pressure chambers 57, 58, connected respectively to the two main pressure galleries 14, 13. The plunger 55 associated with the main pressure chamber 29 connected to the main pressure gallery 13 is however subject on its outer end to the pressure in the other main pressure gallery 14, and vice versa. The inner ends of the plungers 55, 56, are of domed foundation and make substantially point contact with the adjacent faces of the free pistons 37, 38.

The apparatus operates as follows. When the pressure mom of the main pressure galleries 13 (hereinafter referred to for convenience as the high pressure gallery) rises above the pressure in the other'gallery 14 (hereinafter referred to as the low pressure gallery), the free piston 37 in the cylindrical chamber 25 whose outer end is-connected to the high pressure gallery 13 tends to move away from this end of the chamber as shown in the drawings and through the interconnecting'rod 39 forces the second free piston 38 in the same direction against the pressure in the other main pressure chamber 30 connected to the low pressure gallery 14. T he initial movement of the first free piston 37 in this direction causes The ends of the the opening of the control port 41 in this piston to be enlarged to allow an increased flow from the high pressure gallery 13 into the first differential pressure chamber 33 while the relief port 47 is progressively closed. At the same time the control port 42 in the second free piston 38 is closed while the relief port 48 in the second differential pressure chamber 34 is fully opened. to vent this chamber to the relief conduit 49. A pressure is therefore built up in the first differential pressure chamber 33, this pressure being controlled automatically by the movement of the free piston assembly, and consequent variations of the control port openings, to a value which provides a balancing thrust on the piston assembly to counterbalance the out-of-balance forces exerted by the pressures in the two main pressure chambers 29, 39. Since the cross sectional areas of the two free pistons 37, 38, are the same, and the forces on the interconnecting rod 39 are balanced by the balancing plungers 55', 56, the pressure in the first differential pressure chamber 33 is in fact controlled at avalue which corresponds to the difference between the pressures in the two main pressure galleries 13, 14; This differential pressure is transmitted through the pressure selecting valve 32 to the pressure sensitive device 36.

If the pressure in the high pressure gallery 13 relative to the pressure in the low pressure gallery 14 is increased or decreased the piston assembly moves automatically under the'out-of-balance pressures in the main pressure chambers 29, 30, and the openings of the controland relief ports 41, 42, 47, 48, are varied until the pressure in one or otherofthe differential pressure chambers 33, 34, is sufiicient to balance the piston assembly again. It will be understood that if the pressure in the high pressure gallery 13 should fall below the pressure in the low pressure gallery 14 the free piston assembly will move in the opposite direction so that the second differential pressure chamber 34 becomes subject to the differential pressure, while the first differential pressure chamber 33 is connected to relief.

It will also be understood that when the pressure in the high pressure gallery 13 is above that in the low pressure gallery 14, the balancing plunger 55 at the outer end of the first main pressure chamber 29 is urged outwards out ofcontact with the first piston 37, while the other balancing plunger 56 is urged inwards, and-vice versa.

What I claim asmy invention and desire to secure by Letters Patent'is:

1. Hydraulic apparatus for obtaining a differential pressure which varies with variations in the difference between the pressuresin two main pressure lines, com-'- prising a valve including two main pressure chambers connected at relatively remote ends respectively to the two main pressure lines, and a valve piston assembly provided with relatively aligned main pistons having relatively remote end surfaces in the respective main pressure chambers, and including means mechanically interconnecting said main pistons, said surfaces respectively being exposed to the two main pressures in the main pressure chambers so as to urge the valve piston assembly in opposite directions, means defining a first differential pressure chamber, one of said pistons having a first differential piston surface in said first chamber, means defining a second differential pressure chamber, the other of said pistons having a second differential piston surface in said second chamber, the two said differential piston surfaces being directed toward each other and acting in opposition, said pistons respectively being formed with hydraulic conduits from each differential pressure chamber to one of said main pressure lines and to relief; said conduits respectively including fluid control ports formed in said pistons for cooperation with pressure ports, said pressure ports being formed in the respective main pressure chambers and communicating with the respective main pressure lines for controlling'the admission of hydraulic fluid selectively to the appropriate differential chamber, said differential pressure chambers having relief ports positioned for control by the respective pistons to govern the escape of fluid therefrom so as to counterbalance the hydraulic forces acting on the piston assembly, a difierential pressure line, and means for selectively connecting whichever of the two difierential pressure chambers is at any instant at higher pressure to the differential pressure line, and for disconnecting the other difierential pressure chamber from said differential pressure line.

2. Hydraulic apparatus as claimed in claim 1, wherein said valve comprises two hydraulic cylinders each containing one of said pistons, said main pressure lines communicating respectively with the relatively remote ends of the two cylinders, which ends thus constitute the main pressure chambers, the other relatively adjacent ends of the two cylinders constituting the difierential pressure chambers.

3. Hydraulic apparatus as claimed in claim 1, in which said means for selectively connecting the diiferential pressure chambers to the difierential supply line is constituted by a conduit communicating with both said diflerential pressure chambers, and a shuttle valve operatively disposed in said conduit for connecting said difierential pressure lines to whichever of the main pressure lines is at the higher pressure at any instant.

4.' Hydraulic apparatus as claimed in claim 2, in which the two cylinders are arranged in line with one another, and the main pressure chambers are arranged at opposite ends of the two cylinders and the said means interconnecting the two pistons comprises a free compression rod bearing on their adjacent faces, a partition wall between said cylinders, said compression rod making a fluid tight fit with a partition wall between the cylinders, the ends of the compression rod being formed to make substantially only point contact with the pistons, and including pressure balancing plungers whose cross-sectional areas are equal to that of the compression rod, and which are each arranged to make substantially point contact with the remote face of one of the pistons, said plungers being slidably mounted through the relatively remote ends of their respective cylinders and each projecting into and exposed to the pressure of fluid in the main pressure line leading to the main pressure chamber of the other said cylinder.

References Cited in the file of this patent UNITED STATES PATENTS 1,807,040 Leonard May 26, 1931 1,960,466 Trall May 29, 1934 2,547,823 Josephian Apr. 3, 1951 2,634,743 Audemar Apr. 14, 1953 FOREIGN PATENTS 909,482 France Dec. 20, 1945 

